Place the semisweet chocolate chips in a heatproof bowl.
In a small saucepan, heat the heavy cream and instant espresso powder over medium heat until it just begins to simmer. Do not boil.
Pour the hot cream over the chocolate chips. Let sit for 5 minutes, then whisk until smooth and completely melted.
Stir in the softened butter, vanilla extract, and salt until well combined.
Cover the bowl and refrigerate for at least 2-3 hours, or until firm enough to scoop.
Once firm, use a small cookie scoop or a spoon to scoop out portions of the chocolate mixture. Roll into small balls with your hands.
If desired, gently roll the truffles in cocoa powder to coat.
Store the truffles in an airtight container in the refrigerator. Let them come to room temperature for about 15-20 minutes before serving for the best texture.
Notes
These truffles are best enjoyed fresh but can be stored in the refrigerator for up to a week. For a richer flavor, use high-quality chocolate.